1. Field of the Invention
This invention relates to a seal and pressure control arrangement, and more particularly to a compressive seal and actuating arrangement employed in downhole tools for oil well equipment, such as downhole drilling motors to rotate the drilling bit or bits.
The arrangements of the present invention are intended for a drill string in which drilling mud or fluid (a liquid slurry) is passed under pressure from the inlet down to the drill elements of the drill string.
2. Description of the Prior Art
It is well known that effective cleaning of the drilled surface of the bore-hole by high pressure jetting of the drilling fluid increases both penetration rate and drill bit life.
This practice, however, poses major concerns in drilling motors due to the pressure differential created by these jets. Specifically, in oil-lubricated motors, the attendant seals that must withstand such pressure conditions often limit the extent to which this technique may be employed.
The solution, to date, ends with a compromise between the pressure drop experienced across the drill bit and the serviceable life of the motor, i.e., an increase in pressure will lead to a reduced serviceable life of the respective motor. Oil-lubricated drilling motors specify a maximum pressure drop across the bit of approximate 3447.5 Kpa (500 psi). Nowadays, frequently requested, and commonly preferred, however, are pressures in excess of 6895 Kpa (1000 psi), but with present technology and practice, pursuit of more effective jetting of the drilling mud frequently leads to expensive and premature failure of such motors.
Research to date has concentrated on the provision of complicated "super seals" in attempts to obviate the mentioned problems. Most of these are often expensive and generally tend to be unreliable.
According to U.S. Pat. No. 3,169,776-Felt dated Feb. 16, 1965, in machinery including a bore and a central member disposed within said bore and spaced therefrom to define an annular cavity of a transverse cross-section width W about a central member, a resilient packing-ring is disposed. The packing-ring comprises a packing-ring member including an upper surface and having a cross-section having a base portion of width less than W and an upper, deformable, bifurcated portion constructed to delineate an annular recessed area of undercut character which is contiguous with and medially depends from said upper surface and which is conformable to an O-ring snap-seated therein. The O-ring can be snap-seated in the annular recessed area to be protruding above said upper surface. The packing-ring and the O-ring have respective slit interruptions which are mutually displaced.
U.S. Pat. No. 3,297,331-Tracy dated Jan. 10, 1967 shows, for use in an assembly for sealing a rotating shaft within a housing, an articulated spring-holder assembly including an expander ring adapted to engage a seal, said ring being subject to force of a helical spring; a housing encloses the helical spring; and means for articulately connecting the expander ring to said housing so that said seal assembly accommodates vibration, misalignment and run-out.
U.S. Pat. No. 3,342,500-Knudson dated Sept. 19, 1967 is concerned with a composite packing comprising a deformable substantially non-compressible elongated packing member having in transverse cross-section, a base of width W from which extends a bifurcated portion defined by spaced apart legs forming a groove for receiving an O-shaped member, with the surfaces of said legs adjacent the edges of said groove being formed to flare outwardly from a tangential intersection with the inner surfaces of said legs. A deformable substantially non-compressible O-shaped member of a diameter less than said packing member can be snap-seated in said groove in surface contact with the inner surfaces of said legs and normally holds said bifurcated portion spread to a width greater than W. The O-shaped member has a diameter exceeding the length of said legs whereby a portion of said O-shaped member extends from said groove.
U.S. Pat. No. 3,363,910-Toronchuk dated Jan. 16, 1968 relates to a shaft seal for a high pressure pump having a stationary seal member capable of limiting axial and tilting movement and having a rotary sealing member with an inner cylindrical surface spaced from the shaft and an annular member on the shaft projecting outwards with a sealing ring at its apex engaging the inner cylindrical surface on the rotary sealing member. This permits the rotary sealing member to move longitudinally and to tilt with respect to the shaft.
U.S. Pat. No. 4,381,867-Ohgoshi dated May 3, 1983 also relates to a mechanical seal made in a unit construction in which a seal unit case is fitted into and held by the inner periphery of a seal housing in a non-rotatable but axially slidable manner. In the seal housing there is disposed a rotary ring provided on a rotary shaft in a non-rotatable but axially slidable manner. A stationary ring in contact with the rotary ring at the sealing end surfaces thereof is securely fixed to the seal housing. The mechanical seal can be automatically moved to a position where a first fluid and a second fluid are balanced in pressure in response to a difference in pressure between these two fluids.
According to U.S. Pat. No. 4,421,323-Lipschitz dated Dec. 20, 1983, an oil well string member has a cylindrical outer periphery having first and second cylindrical surfaces axially spaced and connected as a tapered ramp. The surfaces are radially inwardly of the outer periphery. The first surface has a smaller diameter than the second surface. A seal assembly is provided along the first surface and arranged to respond to fluid pressure for moving the assembly across the ramp to the second surface and into a sealing position.
U.S. Pat. No. 4,473,231-Tilton et al dated Sept. 25, 1984 shows an arrangement for use in establishing dynamic sealing integrity between a tubular conduit, such as a tubing string, and an in-place tubular seal receptacle, such as a packer, bridge plug or expansion joint, which arrangement includes a multi-unit, multi-element seal assembly. The seal assembly comprises a plurality of seal units with seal units oriented in opposite directions to hold pressure from both ends of the seal stack. The various elements and units of the seal stack are assembled on the exterior of the tubular conduit prior to insertion of the seal stack into the well. Each separate seal unit comprises at least a primary sealing element having a V-shaped cross-section with opposed concave and convex ends and at least one adjacent backup member having a convex surface of the primary elastomeric sealing element. The backup member comprises means for closing off the annular extrusion gap along the bore of the outer seal receptacle. The V-shaped sealing element has a coefficient of expansion greater than the coefficient of expansion of the backup member. The backup member, however, does expand to close off or reduce the extrusion gap along the seal receptacle bore and therefore prevents loss of primary sealing material through the annular sealing gap. The angle defined by inner and outer surfaces on the convex end of the backup member is acute and is normally less than the angle defined by inner and outer surfaces on the concave end of the primary sealing member. Thus when the individual seal units are assembled, the inner and outer surfaces on the concave end of the primary sealing member are not in contact with the inner and outer surfaces on the concave end of the adjacent annular backup member. The primary sealing element is therefore free to flex radially and to expand inwardly and outwardly along the concave end of the V-shaped member.
U.S. Pat. No. 4,496,161-Fischer dated Jan. 29, 1985 is concerned with a radially extensible joint packing with an O-ring assembly having a generally piston-like shape elastomeric body that is radially extensible and has a circumferential groove which retains a circumferentially extensible O-ring.
U.S. Pat. No. 4,506,736-Evans dated Mar. 26, 1985 shows a seal assembly for use in an oil well packer of the type having a packer body having a longitudinal bore, a packer carried on the body for sealing off the annular space between the body and a surrounding well conduit, a mandrel slidably disposed within the body longitudinal bore, the mandrel being spaced-apart from the body to define a fluid flow path between the mandrel exterior and the interior of the body, and wherein the mandrel is slidable between an open, running-in position in which the fluid flow path communicates the annular space above the packer with the mandrel longitudinal passageway and a closed, set position in which the fluid flow path is sealed off. The improvement includes a face seal housing as a part of the mandrel which has a weight loading shoulder and a deformable seal portion. The weight loading shoulder is in the closed, set position to thereby support the weight of the mandrel from the body. A pressure biased seal body for contacting the deformable seal portion when the mandrel is in the closed, set-position to seal off the fluid flow path.
It is known that common sealing elements have certain limitations in high pressure, rotary applications. There exists a point at which pressure and velocity of the respective rotating surfaces combine to generate sufficient heat to cause the sealing elements to fail; the primary source of heat being friction, is dramatically increased by both pressure and velocity.